Cell

• The cell membrane is a selectively permeable barrier that separates the cell from its environment.
• Cholesterol helps to maintain fluidity and stability of the membrane.
• Cell is the structural and functional unit of life - yani forms structures and do functions, Cell is basic unit of Life.
• Robert Hooke discovered cells using microscope
• Outer surface of some cells is covered with non-living and stiff layer called cell wall, Cell wall is present in bacterial, fungal, algal and plant cells.
• Bacterial cell wall is composed of peptidoglycan, fungal cell wall is composed of modified polysaccharide chitin, plant and algal cell wall is composed of cellulose.
• Cell wall is composed of - mainly cellulose, pectin and other polysaccharides and these are cell wall materials which are synthesized by protoplasm, secreted out of cell and deposited on outer surface of plasma membrane.
• Plant cell wall is differentiated into three layers - Middle lamela, primary cell wall and secondary cell wall.
• Middle lamela is the first formed cell plate which works as cementing layer between two daughter cells or adjacent cells yani dono cells ko jode rakhti hai, these two cells are separated when middle lamela dissolves, middle lamela is mainly composed of calcium and magnesium pectates and middle lamela is formed during cytokinesis of cell division.
• Secondary cell wall develops/deposits between plasma membrane and primary cell wall.
• Secondary cell wall doesn't develop/deposit in every plant cell but only develops in hard tissues like sclerenchyma.
• Sclerenchyma is strengthening hard plant tissue.
• cells become dead at their maturity yani full growth.
• Secondary cell wall develops after complete maturation of primary cell wall.
• Secondary cell wall is think and rigid due to decomposition of ligin, inorganic salts and some waxes.
• Secondary cell wall plays important role in plant support i.e supports plant, for example Sclerenchyma fiber, scleroids, xylem vessels and tracheids support plant and have secondary cell wall.
• Cell wall performs two important functions - firstly provides mechanical support, gives definite shape and protection to cell and acts as a skeletal frame work of plants particularly in vascular plants and secondly being hydrophilic in nature, it is capable of imbibing water and thus helps in water movement and solutes towards protoplast i.e cell wall is a permeable structure.
• Skeletal framework means supporting structure.
• Imbibe means absorb
• Permeable means ( of a thing ) allowing things to pass through it.
• All types of cells are enclosed in plasma membrane
• Plasma membrane is outer most living boundary of cells
• Plasma membrane separate cytoplasm from external environment
• All biological membranes have same basic molecular organization, including the plasma membrane, they are composed of a phospholipid bilayer interspersed with proteins means ( Proteins are scattered in them ), The phospholipid molecules are arranged in two parallel layers and their non polar hydrophobic ends face each other and their polar hydrophilic ends are associated with carbohydrates and proteins.
• In some animal cells, cholesterol is 50% out of total lipid molecules in plasma membrane
• Plasma membrane contains several types of lipids like cholesterol, steroids and sterols.
• Sterol is a type of steroid
• Most of the plasma membrane consists of 50% of lipids, 50% of proteins.
• In most of the plasma membrane, carbohydrate portion of glycolipids and glycoproteins is 5 to 10%
• Number of biologists presented different models of cell membrane, one of them was the sandwich model, according to which lipid bilayer is sandwiched between protein layers i.e inner and outer protein layers, this structure is called unit membrane and is present in all cellular organelles but modern technology revealed that lipid bilayer is not sandwiched between two protein layers.
• Fluid mosaic model was proposed by singer and nicolson
• Fluid mosaic model was proposed in 1972
• Fluid mosaic model is a working model of plasma membrane
• In fluid mosaic model, lipid bilayer is retained as core of membrane i.e lipid bilayer is main part of membrane.
• In fluid mosaic model, lipid bilayer's lipid molecules are present in a fluid state and thus are able to rotate, translate and vibrate within the membrane layers
• In fluid mosaic model, lipid bilayer's lipid molecules move laterally within the membrane layers
• Structure and arrangement of membrane proteins in fluid mosaic model is like ice bergs in the sea, the proteins occur as mosaic of discontinuous particles which penetrate deeply and even completely through the lipid sheet
• Penetrate means to put or insert
• Components of plasma membrane are mobile
• Components of plasma membrane are capable of coming together to engage in various types of transient and semipermanent interactions.